Term Labor-Management Relations Act Definition: A Congressional act passed in 1947 that limited the power acquired by U.S. labor unions during the 1930 and into the 1940s. More commonly known as the Taft-Hartley Act, this outlawed unfair labor practices by labor unions to counterbalance earlier legislation that had outlawed unfair labor practices by firms. The Taft-Hartley Act also set up provisions to decertify unions, if members chose to do so, and allowed states to pass right-to-work laws, which would outlaw union shops.